1, Field of the Invention
The present invention relates to a method of forming a layer on a substrate. Particularly, the present invention relates to methods of forming a ruthenium layer on a substrate.
2, Description of the Related Art
A ruthenium metal layer has been researched for use as an electrode material, for example, a gate electrode material for memory devices. Recently, various applications of ruthenium (e.g., as an electrode material for a DRAM and a diffusion barrier for a copper line) have drawn attention. When a ruthenium layer forms an electrode on a structure having a high aspect ratio (e.g., a DRAM capacitor), the ruthenium layer typically should have a thickness of at least about 10 nm. A physical deposition method can be used to form a ruthenium film. An exemplary physical deposition method is a sputtering method, but sputtering tends not to exhibit good step coverage, particularly in high aspect ratio applications like DRAM capacitors.
Chemical vapor deposition (CVD) methods of forming thin films of ruthenium (Ru) or ruthenium dioxide (RuO2) are also known. Such CVD methods use an organometallic compound of ruthenium, such as a ruthenium cyclopentadienyl compound or bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2) and oxygen (O2) gas as reactants. An exemplary method is disclosed by Park et al., “Metallorganic Chemical Vapor Deposition of Ru and RuO2 Using Ruthenocene Precursor and Oxygen Gas,” J. Electrochem. Soc., 147[1], 203, 2000, CVD, employing simultaneous provision of multiple reactants, also suffers from less than perfect conformality.
Atomic layer deposition (ALD) methods of forming ruthenium thin films are also known. Generally, ALD involves sequential introduction of separate pulses of at least two reactants until a layer of a desired thickness is deposited through self-limiting adsorption of monolayers of materials on a substrate surface. For example, in forming a thin film including an AB material, a cycle of four sequential steps of: (1) a first reactant gas A supply; (2) an inert purge gas supply; (3) a second reactant gas B supply; and (4) an inert purge gas supply is repeated. Examples of the inert gas are argon (Ar), nitrogen (N2), and helium (He).
For example, an ALD process can be conducted at a substrate temperature of about 200° C. to about 400° C. and a process pressure of about several hundred mTorr to several tens of Torr, using a ruthenium cyclopentadienyl compound (for example, liquid bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp)2]) and oxygen (O2) gas as reactants. Such a process can form a ruthenium layer having a thickness of about 0.1 Å to 0.5 Å per cycle of supplying the reactants. See Aaltonen et al. “Ruthenium Thin Film Grown by Atomic Layer Deposition,” Chem. Vap. Deposition, 9[1], 45 2003.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form prior art.